We consider linear time-invariant systems subject to real, parametric
variations. The problem of computing the half-sidelength 1/mu_infinity of the
largest stability hypercube in the parameter space is formulated in a
frequency-independent way. The frequency-dependent approach developed in mu
analysis is impracticable, because mu is a discontinuous function of frequency.
We derive an accurate upper bound for mu_infinity, using block-diagonal scaling
of the largest singular value of a real, frequency-independent matrix M. The
optimal scaling is found using quasi-convex optimization. A numerical example
illustrates the method.